1. Technical Field
The present invention relates generally to an improved data processing system and, in particular, to a method and apparatus for representing screen data from a host computer using a markup language.
2. Description of Related Art
Some display devices that are used to present information from mainframe-type host computers have limited capabilities for displaying a user-friendly graphical user interface (GUI). These devices may have a graphic mode, but much of the information is text-only. A host datastream directed to a terminal connected to the host computer, e.g., IBM 3270 and 5250 terminals, typically describes a rectangular host screen image that can be viewed as a character-based structure of fields. The datastream is a shorthand representation for the screen containing both content and formatting attributes. For example, a sequence of 10 blank characters starting from position 100 is described by a repeat command followed by a starting position of 100, an ending position of 109, and a single blank character.
Other platforms that provide user-friendly graphical user interfaces may use host emulation software. However, the information that is received and sent must still conform to the format expected by the host computer. Parsing the host datastream is a major task of a typical host datastream emulation application.
Most emulators avoid redundant parsing by storing the resulting parsed information for later reference. The host screen image information and associated information is stored in an internal data structure or presentation space to support the rendering of the host screen image and the interactions between the two applications at the ends of the datastream.
Some previous solutions to the problems of creating a presentation space have used proprietary programming language structures. For example, Java-based emulation software may represent a presentation space using a Java object while a C-based emulation application represents the presentation space using C structures. Representing a presentation space in a proprietary programming language structure prevents the presentation information from being interchangeable in a multi-product, multi-language, or multi-tier environment.
Proprietary presentation spaces create difficulties in adopting different presentation styles. For example, in a server-based environment, the server can not share a presentation space with its clients. A client needs to establish a special purpose, proprietary communications protocol with the server. The client then requests that the server run a service written to the proprietary presentation space application programming interface (API) in order for the server to retrieve requested information that the client requires to continue its processing. These iterations add significant communications overhead.
Some previous solutions to the problems of creating a presentation space have chosen to duplicate a partial presentation space at the client. This may reduce the communications overhead but locks the application into a specific proprietary protocol and introduces other overhead for maintaining states for two presentation spaces.
In the case of GUI customization for host screens, some previous solutions have typically reconstructed the presentation space information in a proprietary database with additional customizing information for each host screen. The GUI software checks every host screen for matching customizing information in the database to convert it to a different presentation style and maps back user inputs and interactions to keystrokes in the original presentation space. This process incurs the overhead of reconstruction, definition, mapping, and remapping of the same host data in several data structures. Furthermore, the resulting presentation style is locked into a specific customized database that is difficult to migrate to different presentation styles.
In other solutions, an application typically needs to employ the legacy presentation space interfaces and formats. As has become apparent over the past few years, legacy systems may be costly, skill-dependent, and error-prone.
The previous solutions do not present host screen data in a commonly interchangeable format that is easily integrated with other applications and independent of presentation styles. Therefore, it would be advantageous to represent host screen image information in a manner, which is flexible, pervasive, and requires less programming effort. It would be further advantageous for the solution to adhere to open programming and open data standards.
The present invention provides a method and apparatus for representing host datastream screen image information using markup languages. A distributed data processing system contains a network, at least one host computer, at least one client computer, and optionally at least one server. The host computer generates a host datastream containing host screen image information and forwards the host datastream to a client. If the client is not directly connected to the host, then the host datastream may be routed to the client. The host datastream is converted to a markup language tagged datastream at some point within the network according to a Document Type Definition (DTD) authored for the purpose of representing information in host datastreams. The client receives the markup language tagged datastream containing the host screen image information derived from the host datastream and parses the markup language tagged datastream to identify the host screen image information. The host screen image information is displayed on a display device connected to the client, enabling the client to act as an emulator for the host.